High-dynamic-range (HDR) photographs are typically generated by acquiring multiple component images of a scene, each with different exposure levels, and then later, merging the component images into a single HDR image.
Some prior art approaches can involve acquiring a set of, for example, 8 component images, across a range of different exposure levels to ensure that appropriately exposed image information is available for all regions of a HDR image. However, this can involve significant delay in acquiring the component images and so can result in blurring or ghosting artefacts from one image to the next. It can also require a large amount of processing to handle the set of component images.
U.S. Pat. No. 8,724,921, Aptina, discloses a method for capturing a high dynamic range (HDR) image. Multiple component images of a scene are captured at respectively different exposure settings. A further image of an object placed in the scene is captured at one exposure setting. A first radiance image is formed from the multiple component images. A second radiance image is formed from the further image. The first radiance image and the second radiance image are merged to form the HDR image.
Natalia Gurieva “Complete Digital Workflow for HDR Photography”, International Circular of Graphic Education and Research, No. 7, 2014, pp 14-23 discloses capturing a HDR image including conducting a dynamic range evaluation of the scene. Depending on the type of the scene and its dynamic range, different capturing strategies can be applied. For example, in case of midday sun with strong shadows it will be enough to take 3 shots at about 1 to about 1.33 stops apart; inside buildings with some light coming through the windows at least 5 bracketed shots at about 2 stops apart have to be taken.
U.S. Pat. No. 8,687,087, CSR Tech discloses a different approach to capturing an image of a scene which would require high dynamic range including adjusting exposure time on an image block by block basis to maintain a resulting digital signal within a range carried by a digital processing path that carries a limited number of bits.
US 2014/0002694, CSR Tech discloses capturing two or more image frames using different exposure settings and then combining the images to form a single HDR output frame in a video sequence. A pipelined architecture operates on adjacent image frames by performing image alignment, image mixing and tone mapping on the adjacent image frames to generate the HDR image sequence.
It is an object of the present invention to provide an efficient technique for determining appropriate exposure levels for a limited number of component images used to provide a HDR image.